In the fields of deodorization, exhaust gas treatment, and the like, various adsorbent materials have so far been developed. Activated carbon is a representative examples of these, and it has been used widely in various industries for the purpose of air cleaning, desulfurization, denitrification, or removal of harmful substances by making use of its excellent adsorption performance. In recent years, demand for nitrogen has been increasing, for example, in the semiconductor manufacturing process and the like. Such nitrogen is produced from air by using molecular sieving carbon according to the pressure swing adsorption process or temperature swing adsorption process. Molecular sieving carbon is also used for separation and purification of various gases such as purification of hydrogen from a cracked methanol gas.
When a mixture of gases is separated according to the pressure swing adsorption process or temperature swing adsorption process, it is the common practice to separate it based on the difference between the gases in equilibrium adsorption amount or rate of adsorption to molecular sieving carbon or zeolite used as a separation adsorbent material. When the mixture of gases is separated based on the difference in equilibrium adsorption amount, conventional adsorbent materials cannot selectively adsorb thereto only the gas to be removed, and the separation coefficient decreases, making it inevitable that the size of the apparatus used therefor increases. When the mixture of gases is separated into individual gases based on the difference in rate of adsorption, on the other hand, only the gas to be removed can be adsorbed, although it depends on the kind of gas. It is necessary, however, to alternately carry out adsorption and desorption, and also in this case, the apparatus used therefor should be larger.
On the other hand, there has also been developed, as an adsorbent material providing superior adsorption performance, a polymer metal complex undergoing a change in dynamic structure when exposed to external stimulation (see Non-patent Documents 1 and 2). When this novel polymer metal complex undergoing a change in dynamic structure is used as a gas adsorbent material, it does not adsorb a gas until a predetermined pressure but it starts gas adsorption at a pressure exceeding the predetermined pressure. In addition, a phenomenon is observed in which the adsorption starting pressure differs depending on the nature of the gas.
Application of these phenomena to adsorbent materials used in a gas separation apparatus employing a pressure swing adsorption system enables very efficient gas separation. It can also decrease the pressure swing width, contributing to energy savings. Further, it can contribute to size reduction of the gas separation apparatus, making it possible to increase competitiveness in terms of costs when a high-purity gas is put on the market as a product. Moreover, even if the high-purity gas is used in a company's own plant, the costs paid for the equipment requiring a high-purity gas can be reduced, resulting in a reduction of manufacturing costs of the final product.
Known examples of using a polymer metal complex undergoing a change in dynamic structure as a storage material or a separation material are (1) a metal complex having an interdigitated framework (see Patent Documents 1 and 2), (2) a metal complex having a two-dimensional square-grid framework (see Patent Documents 3, 4, 5, 6, 7, and 8), and (3) a metal complex having an interpenetrated framework (see Patent Document 9).
At present, however, further reducing the apparatus size is desired for cost reduction. To this end, further improving the separation performance is desired.
Patent Document 9 discloses a polymer metal complex composed of a terephthalic acid, a metal ion, and 4,4′-bipyridyl. However, Patent Document 9 is completely silent about the effect conducive to separation performance provided by an organic ligand capable of bidentate binding.
Further, Patent Document 10 discloses a polymer metal complex composed of a terephthalic acid derivative, a metal ion, and an organic ligand capable of bidentate binding to the metal ion. However, Patent Document 10 only discloses, in Examples, a polymer metal complex composed of a terephthalic acid, a copper ion, and pyrazine, and it is completely silent about the effect conducive to the mixed gas separation performance provided by an organic ligand capable of bidentate binding.
Further, Patent Document 11 discloses a polymer metal complex composed of a terephthalic acid derivative, a metal ion, and an organic ligand capable of bidentate binding to the metal ion. However, Patent Document 11 only discloses, in Examples, a polymer metal complex composed of a terephthalic acid, a copper ion, and 1,4-diazabicyclo[2.2.2]octane, and it is completely silent about the effect conducive to the mixed gas separation performance provided by an organic ligand capable of bidentate binding.